Vapor phase corrosion inhibition of metals



Patented June 23, 1953 vAPoa PHASE CORROSION INHIBITION or METALS Aaron Wachter and Nathan Stillman, Berkeley,

Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of a Delaware No Drawing. Application May 7,1946, p

Serial No. 668,015

The present invention relates to methods of inhibiting corrosion of metals. More specifical- 137 this invention pertains to novel methods of enclosing metals in materials or containers which contain vapor phase inhibitors. A vapor phase inhibitor may be defined to comprise a compound which inhibits corrosion of metal parts in the presence of water vapor and air (oxygen) because said compound possesses corrosion inhibiting properties and. is capable of vaporizationunder'conditions of use with the resultant presence of these vapors in the vicinity of the metal. More specifically, this invention relates .to the enclosingor packaging of metal objects in a manner whereby corrosion thereof by water vapor and/or aqueous condensates is prevented due to'the presence of said vapor phase corrosion inhibitors.

During storage, handling, transportation, op eration, and use of objects having metalliferous surfaces as for example various metal articles, particularly those of ferrous metals, various steels, aluminum, or alloys of these metals, it is often necessary to prevent the corrosion of these metals when in the presence of water vapor. Heretofore, the various methods tried to prevent such corrosion have been unsatisfactory because such methods did not adequately prevent the corrosion, were cumbersome, did not prevent.

corrosion over a sufficiently long period of time, and/or required an excessive amount of labor and expenditure of time.

It is an object of thepresent invention to provide a novel method for enclosing, packaging, or covering metals whereby the enclosed metal parts are prevented from corroding even when water vapor and/or aqueous condensates are present in such containers. Another object is to provide packaging or covering materials con tainingvapor phase corrosion inhibitors thereby providing adequate corrosion inhibition to metal parts contained therein.

It has now been discovered that enclosing, packaging, or surrounding of metal parts by enclosure in or with vmaterials containing a vaporphase inhibitor, the vapors of which have access-into the thus enclosed space, prevents corrosion of'the metal partseven in the presence of water vapor and oxygen. It was found that the vapor phase inhibitor should preferably have at least a vapor pressure of approximately 0.00002 mm. Hg. at 21 0. Better results are obtainablawith a vapor phase inhibitor having a-vaporpressure greater than about 0.0001 mm.

Hg at 2 1-? C. More rapidinhibition of corrosion.

12 Claims. (01. 21 2.5)

is obtainable with a vapor phase inhibitor having a vapor pressure greater than about 0.001 mm. Hg at 21 C. Also it was found that corrosion of metalparts is inhibited by enclosing them in containers so that the vapors of the vapor phase inhibitor are provided and/or maintained in the enclosed space prior tothe time of substantially complete closing thereof. The process of the present invention maybe applied in a number of Ways which may difierin detail but not in the essentialities-of the invention. Thus, a vapor phase inhibitor may be effectively applied: by placing it as powder or crystals per se, or mixed with inert material, in a container, in which the metal 'part(s) ,to be protected are disposed, by introducing into the container or enclosure a piece of solid, and preferably absorbent material coated or impregnated with the vapor phase inhibitor, by wrapping the metal parts with a wrapping material, such as paper, cloth, cellophane, ethylcellulose, polyvinylbutyral, any sheet material, or the like, which are coated with, or impregnated with the vapor phase inhibitor, and/or by enclosing the metal parts within a covering or packaging material, only one side of which allows disposal of vapors of the contained vapor phase inhibitor to the contiguous atmosphere, as in the case of a waxed paper coated on one side with the inhibitor. A laminated paper or an asphalt paper impregnated or containing one or more of the present vapor phase inhibitors may be used. After providing the containers with the inhibitor in any of the above, or like modes, these packages may then be closed;or.sealed. The resultant package maintained in the package.

Preferably the 'vapors of the inhibitor should have a solubility in water of at least approximately 1% by weight. In some cases the degree of water-solubility may be very low, a true solution may not. result; the vapor phase inhibitor may become incorporated sufiiciently with either water. vapor or liquid water present, and thus may form. a colloidal. sol or a solvate.

A Vapor phase inhibitors .which. have been found applicable according to the present invention include salts of an organic nitrogen base with nitrous acid. Representative classes of nitrogenous bases which are suitable for preparing the present inhibitor-salts include such bases, for example, asr-primary amines,.secondary amines,

present so long as the sum total basicity of the nitrogenous compound is approximately equal to or greater than the acidity of nitrous acid with which it forms a salt. Among the substitu ent groups, the alkyl and cycloalkyl groups are preferred. Secondary amine nitrites, formed from nitrous acid and an amino nitrogen atom attached to a secondary carbon of an organic radical, as typified by di-isobutyl amine nitrite,

tially solid sheet of material, paper, a fibrous composition, or an adsorbent material coated with or impregnated with a vapor phase inhibitor in theproximity of, or .partly in actual contact with, a metal enclosed by a package or other housing or enclosure means. In actual practice it has only been necessary to have the initially applied unvaporized form of the inhibitor suificiently close .to the metal so that vapors arising from the substantially solid or liquid form of the inhibitor transfer sufficiently rapidlyinto theatmosphere contiguous to the metal, thereby inhibitingmetal corrosion. Partial or substantially complete contact of the vapor phase inhibitor (or of compositions containing it) with the metal surfaces of the object di-isopropylamine nitrite, dicyclohexylamine nitrite, piperazine nitrite, morpholine nitrite, or 2,4,4,6-tetramethyl tetrahydro-3-oxazine nitrite are particularly eifective vapor phase inhibitors.

The basicity of the various basic constituents of the class of salts disclosed herein is described,

for example, in The Organic Chemistry of Nitrogen by N. V. Sidgwick, 1937 edition. The many various organic bases are also described'in Organic Chemistry by Paul Karrer, 1938 edition. Various specific examples of organic base nitrites suitable for use in the present invention are described in our copendi'ng application, Serial No. 663,608,'filed April 19, 1946; 7

Table I below sets forth some of the representative organic'nitrogen base nitrites as well as their respective vapor pressures.

TABLE I I Vapor Pres- Compound sure, mm.

1 Hg at 21 C.

1. 2=amiu0 butane nitrite 0038 2. cyclohexylamine nitrite 0027 3. betaphenylethylamine nitrite- 0019 4. 3,3,5-trimethylcyclohexylamine n 0018 5. morpholine nitrite .0030

6. 2,4,4,fi-tctramethyl tetrahydro-3-oxazine nitrite 0017 7. dicyclohexylamine nitrite 00012 8. piperidine nitrite; r .0005! 9. dlbenzylarnine nitrite 00087 10. di-isopropylamine nitrite -1 0047 11 00035 trimethylbenzyl ammonium nitrite Of the above compounds, 'di-isopropylamine nitrite, Z-amino butane nitrite and morpholine nitrite are especially suitable vapor phase inhibitors of the present invention because of their relatively high vapor pressures, theirrelatively higher solubility in water, and in view of the fact that a higher vapor pressure of the inhibitor results in a morerapid distribution of its vapors throughout the contiguous atmosphere.

The concentration of amounts of the vapor phase inhibitor which is employed to inhibit corrosion of a metal under the above specified conditions may vary-within wide limits, but it is preferred to apply the smallest effective concentration. This is usually between about 0.1 gm. to about 5.0 gm., and. preferably approximately 1.0 gm. of the vapor phase inhibitor present per square foot of the inner container surface. Especially satisfactory results are attained when the inhibitor is provided in such concentration as to allow between about 1.0 gm. and about 15 gm (or for average conditions about '6 gm.) thereof for each cubic foot of enclosed vapor space. These specified concentrations of 'inhibitor may be obtained by placing a SllbStanto be protected (e. g. when a thin film or coating. of the vapor phase inhibitor is deposited upon a metal) and then packaged, achieves the present invention more effectively and economically in' that the metal is protected with more certainty, completely and immediately, and in that somewhat less inhibitor may be required. In this connection, a metal article coated with a vapor phase inhibitor, when enclosed within a package or container, willgradually set up an equilibrium with the vapor or gaseous phase of the enclosed space, and with the packaging ma-;

terial, no matter how small the enclosed gascontaining space. At equilibrium, substantially the sarneresult is achieved as if the interiorwalls of the enclosing box or package had been coated with the vapor phase inhibitor instead-of the inhibitor coating being initially on the metal. The main difference is however, that the closer the vapors or the solid form of the present inhibitors are to the surface of a metal, the more quickly there is attained a complete inhibition of corrosion. Where an enclosing-material impregnated with one or more of the present in hibitors is not applied to cover a metal, as for example when the inhibitorecontaining material is simply placed in or, distributed throughout the interiorspace enclosed by a container, satisfactory inhibition of corrosion is attained by'applying approximately 1 gm. to 15 gm., or usually about 6 gm., of an unvaporized form of the in hibitor per. cubic foot of enclosed vapor space.

However, lesser concentrations of the inhibitor may give satisfactory results under milder conditions. As a minimum requirement, an atmosphere containing at least-some of the vapor of the inhibitor must be present in contact with a metal. Better results are obtained by having the metal article surrounded with an atmosphere which is approximately saturated with the vapor of the inhibitor.

Stability of the present vapor phase inhibitors, and particularly the stability of organic nitrogen base nitrite salts, is adversely affected by an environment which, on contact with or dispersion in water, yields a solution having a pH of less than-about 5. In some instances the stability is also adversely affected by elevated temperatures, such as F. or F. Such factors, or others which may render an organic nitrite salt unstable, are greatly lessened or en' tirely obviated by introducing an alkaline agent either into the inhibitor per se or into the vapor space containing the vapors of the inhibitor. This addition of the alkaline agent to the un volatilized portion of the vapor phase inhibitor is particularly applicable in caseswhere the inhibitor has a tendency to decompose. Suitable stabilizing agents include organic or inorganic hexylammonium bicarbonate, sodium carbonate,

sodium 'chromate, sodium phosphate, isopropyl urea, or piperazine.

The particular stabilizing agent, and the .optimum quantity thereof required to be effective depends on a number of'vari'ables. In general, between about 0.1% and about of a stabilizer by weight of the vapor phaseinhibitor) are effective. It willbe seen from the'above that many alkaline materials have been found to be effective in stabilizing a saltof an organic nitrogen base with nitrous acid. In this respect any organic or inorganic compound which is capable of removing acidity or maintaining an alkaline condition is suitable as the stabilizing agent.

The vapors of amine nitrite salts may contain, and in a number of cases-have been found to contain, vapors of the corresponding nitrosamine; In studies-on stabilityit wasfound that the decomposition of some secondary amine nitrite salts was of an autocatalytic type. De composition of such an amine nitrite was also accelerated by small amounts-of water. Such decomposition as a whole, however, was readily prevented by the presence of an alkaline agent of the class defined above.

It was stated above that an amine nitrite salt may be in equilibrium with'the nitrosamineand water which are formed from the corresponding nitrite, and that the'shift of the'equilibrium toward the nitrosamine is increased at increasingly higher temperatures. This equilibrium may be stated as follows:

' Heat on R2NH'HNO2 .2 RzNN=O H20 wherein R represents an organic radical. According to the usual laws of equilibrium, .anexcess of either water ornitrosa-mine or both above the chemically equivalent amounts indicated in the above equation tends to force the equilibrium toward increasing concentrations of the amine nitrite. The presence of the'nitrosamine is not detrimental to vapor phase corrosion inhibition; in fact, vapors of the nitrosamine itself were found to inhibit corrosion ofmetalin the presence of watervapor, However, in a number of cases they did notappear as effective as vapors of the corresponding amine nitrite salts when the latter were 'substantiallyfree of nitrosamine.

The present vapor phase inhibitors can be applied either separately or in various .mixtures of members of this-class, or with other vapor phase inhibitors. In certain cases it is advantageous to applya mixture of'inhibitors containing an inhibitor with a 'relativley high vapor pressure and an inhibitor with a relatively low vapor'pressure. In this way the highly volatile inhibitor more rapidly protects metals in its vicinity, whereas the less volatile inhibitor gradually builds up an atmosphere saturated .with its'vapor. Thelatter is either substantially not lost or onlyzlost to .a slight degree due to partial permeability of an enclosure, whereas the highly volatileinhibitor may escape {roman enclosure to a relatively greaterdegree than the inhibitor having a lower volatility. Once initial rapid inhibition of corrosion by the highly volatile inhibitor hasbeen provided, usually the best overall long-term inhibition is provided by an atmospheresufiiciently concentrated with an inhibitor having a relatively lower volatility, such as dicyclohexyl ammonium nitrite.

The vapor phase inhibitors of the present invention, whether as such, or disposed on or in inert substances, upon contact with water or dispersion therein should preferably yield a solutionhaving a pH of at least about 6 Alkaline agents, either volatile or non-volatile may be used with the present inhibitors to maintain the desired pH.

The vapors of organic nitrogen salts of nitrous acid are more effective in preventing aqueous corrosion of various 'ferrous'metals, e. g., steels, as well as couples of steels with aluminum or copper or other metals, and aluminum and alloys of these metals. More satisfactory inhibition of corrosion of copper, and copper alloys, such as brass and bronze, is obtained when small amounts of volatile carbonates, suchas ammonium carbonate or an organic nitrogen base carbonate, for example, di-isopropylammonium bicarbonate or dicyclohexylammonium bicarbonate, are presentin the vapor phase along with the inhibitor.

Various techniques have been practiced in the utilization of the vapor phase inhibitors disclosed herein. Within any enclcmure means, preferably comprising a substantially impermeable material, corrosion of metal surfaces by moisture is prevented by enclosing, or making available therein, a vapor phase inhibitor. The latter can be originally introduced as a solid, a liquid, or a vapor, or in solution, as an emulsion, or a dispersion, etc., as long as the inhibitor may vaporize and thus be present in the atmosphere around the metal. In the alternative, the inhibitor may be introduced as a vapor. In the caseof enclosed metal articles, the inhibitor may be disposed as crystals or as a powder in various porous containers; or the metal article or the wrapping material thereof may be coated with material containing the vapor phase inhibitor. In one of the preferred embodiments of the invention it was found advantageous to use wrapping material, such as paper which was first impregnated'with the vapor phase inhibitor. In another embodiment, waxed paper was warmed to melt or soften the surface layer of one side thereof and crystals or powdered di-isopropyl ammonium nitrite, or the like were then sprinkled upon the partially melted wax. The latter was cooled, and the excess vapor phase inhibitor was shaken off. The resulting Waxed paper coated with the vapor phase inhibitor was found to be an effective supplier of corrosion-inhibiting va-- pors. Absorbent materials such as paper, cotton, wool, cloth, silica gel, alumina gel, fullers earth, asbestos, and activated carbon are some examples of materials which can be impregnated with theabove vapor phase inhibitors. In cases wherein free circulation of air is prevented around metal articles in storage, the presentinhibitors are effectively applied by introducing them as vapor, or by providing an atmosphere containing inhibitor vapor around such metal articles. Corrosion by'circulation of air over metal surfaces can be ly saturating the introduced air with vapors of the present inhibitors. be coated with the vapor phase inhibitor by de positing the latter from a solution or a dispersion or from heated vapors contacting the metal, or by incorporating the inhibitor in relatively non-volatile coating materials. The latter may be a paint, a resin, a varnish, a lacquer, etc.

The present invention also includes the en-' closing or making available of the vapor phase inhibitors within th vapor spaces present within or enclosed by machines, mechanisms, or metalarticles of manufacture. Prevention of corrosion from the vapors and/r liquids present within the spaces enclosed by various hydraulic mecha-' nisms, may be secured for instance by the introduction of one or more'of the vapor phase inhibitors into a liquid hydraulic fluid. Aerosols and the carriers used therewith are also effective 'ing examplesare percentages by weight unless otherwise specified. 1

Example I 7 Seven steel bolts, each of which was T inch in diameter and 3 inches long, were solvent washed,

. electrolytically cleaned, and the threaded ends inserted into corks. These corks were then used as, stoppers for 2'-ounce bottles. In this way the bolts were suspended in thevapor space of these bottles. Six of the bolts were suspended in bottles each of which contained 0.2 ml. of distilled water and 0.2 gm. of avapor phase inhibitor. The bottle containing the seventh bolt was provided with 0.2 ml. of distilled water only. The bolts were not in contact; with the walls, bottom or liquids contained inthesample bottles. The vapor phase inhibitors thus tested in the respective bottles were: di-isopropylamine. nitrite, morpholine nitrite, cyclohexylamine nitrite, piperidine nitrite, dibenzylamine nitrite, dicyclohexylamine nitrite. For a period of 14 days'all of the bottles were subjected to alternate heating and coolingcycles, each bottle being, heated to 50 C. for a period of 10 minutes, followed by cooling to 0 C for 10 minutes and then permitted to stand at room temperature. Three such cycles were carried out during each day of the test. At the end of this 14-day test period, examination of all of the seven bolt specimens showed that only the seventh specimen (which had'not been subjected to the vapors of one of the amine nitrites), was badly rusted. The test with thesixth specimen in which dicyclohexyl- 1 Two steel-bolt specimen were given the same prevented by substantial Metal objects can also sample bottle there was placed a folded pad of kraft paper,.in each instance amounting to 8 square inches ofthe'paper. In one of the bottles,

the kraft paper had absorbed therein 0.1 gm. of di-isopropylaminenitrite and 0.1 ml. of distilled water. .In the other bottle the paper had absorbed therein only 0.1 ml. of distilled water (without any vapor phase inhibitor being present). These two specimens weresuspended in the respective bottles, stoppered tightly; and subje'cted to the alternate heating and cooling cycles described in Example I for a period of '37 days. At the end of this test period, it was found that the specimen disposedin the bottle containing the vapor phase inhibitor was preserved in its original appearance. On the other hand, the other specimen was so severely rusted that very little of the surface of thissteel bolt was visible; in -fact,-over of said bolt was covered with a heavy growth of rust.-

Example III Two steel bolt specimens were prepared by solvent washing, followed by Wire brushing and then screwed intothe fitting nut just far enough that,

the latter acted as a supporting base in which the bolt stood in a vertical-position. Each of the amount of distilled water, but withoutany vapor phase inhibitor, was absorbed in the same manneron a piece of cotton inserted into-a prepared recess of the cork of the other of the two bottles. The respective bolts were not in contact with the cotton or the materials absorbed in the cotton. These corked bottleswere allowed to standat normal room temperaturefor a period of '76 days. At the end of this test period, the steel specimen which was subjected to the action of morpholine nitrite vapors was free from rust. The surface of this steel specimen was shinya's 'it had been at the start of the test. on the other hand, the other steel specimen was so severely rusted that the surface of it had a rusty appearance and had lost its original hiny polished surface.

. Eaccmple IV 1 Two 1%; inch low carbon steel plates were machinedto a /4 inch by 3 inch strip and wire brushed to a bright metallic sheen. .An inner wrap of neutr'alkraft paper and an outer wrap of laminated metal foilpaper provided with aninternal coating of a thermoplastic resin was provided around one of the desc1'ibed-steelplate specimens. The outer lamina-ted metal foil wrap was heat sealed. The other steel plate was packaged in the identical manner except that the inner wrap or the neutral kraft paper, which in each instance measured2 inches bye inches, was impregnated by dipping it in-a; 50% (by weight) aqueous solution of. morpholi'n'e nitrite. After dipping, the paper was dried by suspension for about 10 minutes in an' air blast maintained at approximately 50 C. Aftersuch drying, the kraft paper contained approximately 0.1 gm. of the inhibitor. Y

Botli' specimens; after. packaging, were im-:

i rsedzinsynt et cseawa e prepa aqcp d e to U. 15 Bureau "of Ships Specification 14-0-15 (IN'IJ) (1943), for aperiod of 26 days, the water being maintained at a temperature of approximately 30 C. during the test. At the end of the test period these packages were opened. It was discovered that the steel plate wrapped in paper which did not contain any amine nitrite was badly corroded with rust. On the other hand, the; steel plate packaged with the amine nitrite in th inner wrap retained its original polished and junblemished condition and appearance.

Example V A test similar to that described in connection with Example II was made with an assortment ofjsteel nuts, screwsand bolts in twosmall paper cardboard boxes, by 1%- by 2% inches. A liner was made for each box, one of untreated kraft paper, and the other of kraft paper impregnated with approximately 0.14 gm. of di-isopropylammonium nitrite. The top of the box was made of clear cellulose acetate sheet to allow observation of the contents. A small hole approximately inch in diameter was punched in the cellulose acetate window of each box in order to allow ample breathing. These two boxes were alternately chilled to 5 C. and warmed to 30 0. several times a day for six weeks. After this periodof time it was found that considerable rust was evident on the steel parts in the box containing the untreated kraft paper liner, but that there was no rust on the steel parts in the box lined with the paper containing di-isopropylammonium nitrate.

Example VI A by 3 inch specimen of aluminum was wrapped in 2 by 4 inch pieces of kraft paper impregnated with di-isopropylammonium nitrite which was then placedin another envelope made byfolding 5 by'5 inch pipeces of Grade A paper; the lastenvelope was then sealed with a pressuresensitive, waterproof tape. Another aluminum specimen was similarly prepared, the only difference being that it was wrapped in an untreated piece of the said kraft paper. The envelopes or packages thus produced were suspended over'the water at 30 C. for 2 months, whereupon it was found that, whereas the aluminum specimen wrapped in the paper treated with di-isopropylammonium nitrite was not corroded, the aluminum specimen wrapped in the untreated paper had considerable white corrosion.

Example VII A number of tests were effected: In each case a low-carbon steel specimen, inch by 2 inches, was first cleaned electrolytically, neutralized with sodium carbonate, rinsed in distilled water, and then dried by carefully rinsing with acetone and drying. The steel specimen was then weighed and suspended in the vapor space of a 125-ml. bottle by means. of a glass hook placed in a cor]; fitted intothe underside of a hollow stopper. One-half gram of the compound to betested and 0.5' of distilled water were placed at, the bottom of each bottle (maintained in the upright position) and then the stopper with the attached steel specimen was put into place. This stopper was sealed. with a silicone stopcock grease. The thus-prepared bottle and contents were maintained at 150 F. for 7 days after which thespeci- 11.0 in-a vacuum desiccator and the weight changes determined. The following results were obtained:

Approximate Gain in l inhibitor Weightv gmtectioAn of (in Giams) ur ace rea Against Rusting None .0579 5% protection.

o. .1022 0 D tSietcondary butylam nonimn .0026 protection.

1 e- Di-Gyclohexylammonium nitrite .0101 99% protection. Di-Isopropylemmonium-nit .0052 90% protection.

.0163 Do. Guanldiniuni-Nitrit 0008 Do.

Example VIII 0.1 gm. pieces of 60 lb. 'kraft paper were immer'sed in a 2% by weight solution of discyclohexylamine in 75% methanol-25% water solvent mixture for 10 seconds and then dried 5 minutes with warmair. One drop of 0.01 N sulfuric acid solution added to an entire extract of such treated paper changed phenolphthalein indicator over to the acid side. A sample of the described amineimpreg-nated paper was then tested in a sealed glass tube stability test wherein 0.1 gm. of the paper onto which was deposited 0.05 gm. of dicyclo'hexylammonium nitrite, was subjected to the vapors from 0.50 ml. of water. A tube for a control test was prepared using a sample of the untreated paper. After the testing periods indicated below, the contents of the tubes were analyzed for nitrite content, and the following results were, obtained:

Percent of Nitrite Ions Present Untreated Paper ,Eaxample'IX ,One tenth of a gramof di-isopropylammomum. nitrite containingpr intimately admixed with 10 per cent by weight of sodium bicarbonate was impregnated into 8 square inches of kraft paper, placed inthe bottom of ,a glass bottle, and 0.1 ml. of distilled water added. ;In the vapor space of this wideymouth bottle, a steel bolt was suspended by attaching it to the stopper of the bottle. The steel'bolt specimens used in such a test were given the same preparatory treatment as that described for Example 1. Control experiments on untreated kraft paper were run under the same conditions side by side for comparison. Twice each day the described sealed bottles with their contents were chilled to 0 C. for 20 30 minutes, warmedto 50 C. for 5 minutes and allowed to stand at room temperature (about 25 C.) the remainder of the, time. The steel bolt in the stoppered bottle containing untreated kraft paper rusted duringthe first day of the control test, but the steel bolt in the stoppered bottle containing the kraft paper impregnated with 0.1 gm. f;di -isopropylammonium nitrite containing 10 perpent by weight of sodium bicarbonate did not rust-afterfour weeks of being subjected .to the cycles ofthis test.

Example X Tests were conducted to show the effect of mensiw reremoved, wa hed w awi n d i d m nansr 1011 5 91. t e-stab li Q d -i o ammonium nitrite.

' of at least about 6.

Four-ply spiral-wound kraft paper tubes, '18 inches long and 0.75 inch outside diameter were used in these tests. The layers of the paper tubes were held together with casein glue, the pH of the tube was 9.4 and titration to a pH of 7 of the water extract of these paper tubes before impregnation showed that on the average each one of them contained approximately 0.002 equivalent of basic-reactingmaterial. The conditions of operation and the results obtained are summarized below.

A -inch section of the hollow 4-inch diameter paper tube impregnated with a volatile organic amine nitrite to be tested was placed in a 1 by 6 inch Pyrex test tube. A inch by 5 inch steel strip was placed inside the paper tube, and the glass container test tube thereof was stoppered and maintained one hour at 120 F. Just before testing, the steel strip was polished with No. 2/0 emery paper. The test was continuedfor one hour at 120 F., and then the solid stopper was replaced by a cork stopper having a inch diameter hole, the test tube being then suspended open end downv in a standard humidity cabinet held at 100 F. and 90% humidity. The results obtained are summarized in the following table:

corrodible by contact with water vapor and oxygen, the step of enclosing said metal within a fibrous material containing a secondary amine nitrite having a vapor pressure of at least about 0.0001 mm. Hg at 21 C., said nitrite being present in an'amount suflicient tomaintain .a corrosioninhibiting atmosphere which, upon dispersion in water, yields a solution having a pH-value of at least about 6.

4. In a method for'pack'aging a metal normally corrodible by contact with water vapor and oxygen, the step of enclosing said metal within a substantially solid covering material containing a secondary amine nitrite salt having a vapor pressure of at least about 0.0001 mm. Hg at 21 0., said nitrite being present in an amount sufficient to maintain a corrosion-inhibiting atmosphere which, upon dispersion in water, yields a solution having a pH value of at least about 6.

a 5. In a method for packaging a metal normally corrodible by contact with water vapor and oxy gen, the step of enclosing said metal within a substantially solid covering material containing an organic nitrogen-base nitrite having a vapor pressure of at least about 0.0001 mm. Hg at 21 C., said nitrite being present in an amount sufficient Amt. Im- Appearance at Time in Hours Vapor Phase Inhibitor ggfgggggi i I lengthtube b 100 200 300 400 500 700 Grams Di-isopropyl ammonium 3. no rust-.- no rust no rust no rust no rust no rust.

nitr' e. Di-cyclohexyl ammonium 1.6 -..do .do -do. ..do ..do Do.

nitrite. None (control) rusting on fine rust on faces, slightly more very little little change... little change.

edges. edges progressive rust. change.

rusting.

e Tube impregnated with 20% solution di-cyclohexylamine nitrite in methyl alcohol.

b The lower one inch of tubes were moist.

As is apparent from the results, in the above table, control steel specimens'in paper tubes not impregnated with volatile corrosion inhibitors were rusted considerably evenafter the first few days of treatment. After 400 hours exposure, no rust was present on any of the steel specimens in the di-isopropylammonium nitrite-impregnated paper tubes. After 700 hours, the steel specimens in the di-isopropylammonium nitrite-impregnated paper tubes were free of rust. After this length of time (700 hours), there was no rust present on the steelspecimen inside the paper tube impregnated with di-cyclohexylammonium nitrite.

The present invention is a continuation-impart of the copending application Serial No. 557,358, filed October 5, 1944, now abandoned. l

We claim as our invention: q p

1. In a method for packaging a metal normally corrodible by contact with water vapor and oxygen, the step of enclosing said metal within a fibrous material containing dicyclohexyl amine nitrite in an amount suflicient to maintain a corrosion-inhibiting atmosphere which, upon disper sion in water, yields a solution having a pH value 2. In a method for packaging ametalnormally corrodible by-contaot with water vapor and oxygen, the step of enclosing said metal within a fibrous material containing .di-isopropyl amine nitrite in an amount suflicient to maintain a corrosion-inhibiting atmosphere which, upon dispersion in water, yields a solution having a pH value of at least about 6.

3. In a method forenclosing a metal normally to maintain a corrosion-inhibiting atmosphere which, upon dispersion in water, yieldsa solution having a pH value of at least about 6.

6. The combinationjcomprising a metal article normally corrodible by contactwith water vapor and oxygen and a fibrous material enclosing said metal article, said fibrous material containing dicyclohexyl amine nitrite in an amount sufficient to maintain a corrosion-inhibiting atmosphere which, upon dispersion in water, yields a solution having a pH value of at least about 6.

7. The combination comprising a metal article normally corrodible by contact with water vapor and oxygen and a fibrous material enclosing said metal article, said fibrous material containing diisopropyl amine nitrite in an amount sufficient to maintain a corrosion-inhibiting atmosphere which, upon dispersion in water, yields a solution having a'pH value of at least about'6.

8. The combination comprising a metal article normally corrodible by contact'with water vapor and oxygen and a fibrous material enclosing said metal article, saidfibrous material containing a secondary amine nitrite having a vapor pressure of at least about 0.0001"mm.' Hg at 21 C., said nitrite being present in an amount sufiiicient' to maintain a corrosion-inhibiting atmosphere which, upon dispersion in water, yields a solution having a pH value of at least about 6.

9'. The combination comprising a metal article normally corrodible'by contact with water vapor and oxygen and a substantially solid covering material enclosing said metal article, said covering material containing a secondary amine nitrite having -a,- vapor'pre'ssure of at least-about'0.0001

mm. Hg at 21 C., said nitrite being present in an amount sumcient to maintain a corrosioninhibiting atmosphere which; upon dispersion in water, yields a solution having a pH value of at least about 6.

10. The combination comprising a metal article normally corrodible by contact with water vapor and oxygen and a substantially solid covering material enclosing said metal article, said covering material containing an organic nitrogen-base nitrite having a vapor pressure of at least about 0.0001 mm. Hg at 21 C., said nitrite being present in an amount sufficient to maintain a corrosioninhibiting atmosphere which, upon dispersion in water, yields a solution having a pH value of at least about 6.

11. In a method for packaging a metal normally corrodible by contact with water vapor and oxygen, the step of enclosing said metal within a fibrous material containing an N-hydro- V carbyl ammonium nitrite salt having a vapor pressure of at least about 0.00002 mm. Hg at 21 C., said nitrite salt being present in an amount sufiicient to maintain a corrosion-inhibiting atmosphere which, upon dispersion in water, yields a solution having a pH value of at least about 6.

12. The combination comprising a metal article normally corrodible by contact with water vapor and oxygen, and a substantially solid covering material enclosing said metal article, said covering material containing an organic ammonium nitrite salt having a vapor pressure of at least about 0.0001 mm. Hg at 21 C., said nitrite salt being present in an amount sufiicient to maintain a corrosion-inhibiting atmosphere which, upon dispersion in water, yields a solution having a DH value of at least about 6.

AARON WACHTER. NATHAN STIILMAN.

References Cited in the file of this patent UNITED STATES PATENTS v OTHER REFERENCES Ex parte Appeal Number 5286, April 4, (Case No. 213) 29 J. P. S. 456. 

12. THE COMBINATION COMPRISING A METAL ARTICLE NORMALLY CORRODIBLE BY CONTACT WITH WATER VAPOR AND OXYGEN, AND A SUBSTANTIALLY SOLID COVERING MATERIAL ENCLOSING SAID METAL ARTICLE, SAID COVERING MATERIAL CONTAINING AN ORGANIC AMMONIUM NITRITE SALT HAVING A VAPOR PRESSURE OF AT LEAST ABOUT 0.0001 MM. HG AT 21* C., SAID NITRITE SALT BEING PRESENT IN AN AMOUNT SUFFICIENT TO MAINTAIN A CORROSION-INHIBITING ATMOSPHERE WHICH, UPON DISPERSION IN WATER, YIELDS A SOLUTION HAVING A PH VALUE OF AT LEAST ABOUT
 6. 